This invention relates generally to electric motors, and in particular to a switch for starting an electric motor that inhibits vibration and associated noise during operation of the motor.
Capacitor start and split phase induction motors, such as motors used in appliances (e.g., clothes dryers), typically have a run winding and a starting winding placed in a stator assembly. The starting winding is energized during start-up of the motor, or when the speed of the motor falls below a specified operating speed, so as to create a rotating field in the stator and to apply sufficient torque to the rotor for starting purposes. However, once the motor has accelerated to a desired operating speed, or a predetermined percentage thereof, the rotor is able to follow the alternations of the magnetic field created by the run winding, and the starting winding is no longer needed. The starting winding is not intended for continuous use and may fail if not de-energized during normal operation of the motor. Consequently, a two-position starting switch is provided with the motor for energizing the starting winding only during start-up of the motor and for de-energizing the starting winding once the motor has attained its desired operating speed. Reference is made to co-assigned U.S. Pat. No. 4,296,366, U.S. Pat. No. 5,744,883, and U.S. Pat. No. 6,184,484, each of which is hereby incorporated by reference, for additional detail regarding switches of this type.
These motor starting switches are conventionally actuated by a centrifugal actuator mounted on and rotatable with the rotor shaft of the motor. The centrifugal actuator is responsive to the speed of the motor for actuating the starting switch from its start to its run position in response to the motor attaining a predetermined operating speed. The centrifugal actuator engages a lever of the switch and moves the lever to change one or more electrical contacts in the switch. The lever pushes one or more metallic spring arms into or out of contact with corresponding electrical terminals, thereby energizing one of the windings and de-energizing the other winding. Typically, the lever pushes the spring arm at the start position of the switch, and releases the spring arm at the run position of the switch. Unfortunately, the lever has a tendency to vibrate and create a rattling noise during normal operation of the motor. At its run position, the lever does not carry a substantial load and, due to design tolerances, is free to move a small distance within the switch. That permits the lever to oscillate, at a frequency depending on the motor, and engage nearby parts which produces an objectionable noise. The tendency to vibrate is aggravated by the lever being made of a lightweight material such as plastic.
In response to that tendency, some manufacturers have installed a coil spring inside each switch. The spring urges the lever toward engagement with another component, such as an external wall of the switch housing, so that the lever remains generally stationary when at its run position and does not rattle. The force of the spring may be readily overcome by the centrifugal actuator for moving the lever to its start position. Unfortunately, the coil spring adds cost, increases complexity during manufacture, and degrades reliability of the switch.
Among the several objects and features of the present invention may be noted the provision of a switch for an electric motor which inhibits vibratory noise; the provision of such a switch which is reliable in operation; and the provision of such a switch which is economical to produce.
In general, a switch according to the present invention is for an electric motor. The switch comprises a housing including a wall and an electrical terminal within the housing. A flexible switch arm has a fixed end secured within the housing and a free end movable between a first position in which the arm engages the electrical terminal making an electrical contact therebetween which affects operation of the motor, and a second position in which the arm is spaced from the electrical terminal and free of the electrical contact. A movable control is engageable with the switch arm to actuate movement of the switch arm between the first and second positions. A biasing member is for urging movement of the control toward a generally stationary position against the wall of the housing to inhibit vibration of the control during operation of the motor. The biasing member is attached to the switch arm.
In another aspect, the present invention involves an improved switch for an electric motor having a wall defining a housing and an electrical terminal in the housing. A flexible switch arm has a fixed end and a free end movable between a first position in which the arm engages the electrical terminal making an electrical contact affecting operation of the motor and a second position In which the arm is spaced from the electrical terminal. A pivotally mounted lever is engageable with the switch arm for movement of the switch arm between the first and second positions. The improvement comprises a cantilevered spring attached to the switch arm and engaging the lever to urge the lever toward a generally stationary position against the wall of the housing to thereby inhibit vibration of the lever during operation of the motor.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.